magnetic effect of electric current jee mains and neet

 

Magnetic Effect of Electric  Current 

jee mains

Electric Current:Can produce heating effect Now other effect of electric current is it can be produce magnectism or magnetic effect.

Magnetic effect of electric current flowing in a wire produce a magnetic field around it.

 

A magnet is an object which attract piece of iron ,steel ,nickel ,cobalt IN OF FREELY suspended which towards north  direction called south pole and south direction called south pole like magnetic poles repels each other whereas unlike magnetic attract each pole.

 

Use of Magnet:In children toys ,radio and speaker ,refrigerator door ,in medical theropy  ,magnetic resonance imagine,and in the production of electricity .

Magnetic Field:Has an electric charge creates an electric field in same way a magnet create an magnetic field around it.

 

The space surrounding a magnet in which magnet force is exerted is called magnetic field.

 

 

Magnetic Field Lines-

Magnetic field lines live north pole of an magnet enters to its south pole .]

 

The strength of magnetic field line is indicates by the degree of clossness of magnetic field  line.

AT the pole field ines are closet together ,magnetic field is strongest  at the poles.

 

ü CHARACTERISTIC OF MAGNETIC FIELD LINES  IMPORTANT  Topic

1)The magnetic field line is originated from north pole of magnet and ends at its south pole .

2)Magnetic field lines comes closer to one another near the poel of magnet but they are widely separated at other places .

3)Magnetic fields lines are never intersect.

 

Experiment to demonstrate magnetic effect of current------------Important

1)Take a long straight copper wire ,two or three cell of 1.5V each plug key and connect them in series .

 

2)Place the  straight wire over and parallel to compass needle .

3)Plug the key in the circuit.

4)If a current flows through north to south observe the needle of compass that deflects towards east.

5)Replace the cell connection as shown in figure current is flowing from south to north and compass needle deflects towards west.

 

Note:If we change the direction ,the direction of magnetic also change.

 

 

                   Magnatic field due to a current through a straight conductor wire

 

The magnetic lines around a straight conductor carrying current are concentric circles ,whose centrialise on the wire.

We have straight vertical wire current flows through bottom to top produces a magnetic field around a wire which can be shown by sprinkling iron fillings on the cardboard ,iron filling gets magnetic and arranged themselves in circle around the wire .

This shows that magnetic field lines are circular in nature around the wire or conductor .

2)Magnetic field lines will be in anticlock wise and vise versa .

Note:

1)Magnetic field directly proportional to the amount of current passing in straight wire .

2)Magnetic field will be inversely proportional to the distance of that point from wire .

 Right hand thumb Rule

According to maxwell Right hand thumb rule -Imagine that you are holding current carrying wire in right hand so that  your thumb point in the direction in which your fingure in circle wire will give the direction the magnetic field lines around the wire.

Maxwell right hand thumb rule is also known cork scruve rule .

Note:

1)When the flow of electric current vertically upward the direction magnetic field is in anticlock wise.

2)When the electric current flows vertically downward then the direction of magnetic is in clock wise.

 

·    Magnetic field due to a current through a circular loop

1)A circular loop are circular wire is fixed to a thin cardboard sheet when a current pass through a circular loop of wire a magnetic field is produced around it.

Magnetic field of lines are circular near the current carrying ‘loop .as we know magnetic fields line become bigger and bigger .at the centre of circular loop magnetic fields lines are straight at the point ,.By applying Right had thumb rule it can be seen is segment of circular loop carrying current profuced magnetic field line in the same direction within the loop at the centre of circular loops all the magnetic field lines are in the same direction and add each other due to which strength of magnetic filed increases .

Note:

1)The magnitude of magnetic field produce by the circular loop at the centre is

i)directly proportional to the current passing through the circular loop.

ii)Inversly proportional to the radius of circular loop.

Now we can conclude that strength of magnetic field produce by current carrying circular wire can be increased.

 

1)By increasing the no. of tonnes coil.

2)By increasing the current passing through loop.

3)By decreasing the radius of loop of coil.

 

Ø    Magnetic field due to current in solenoid

What is Solenoid ?

Solenoid is a long coil containing large no. of close tonnes of insulated copper wire .

 

When electric current is passed through the  solenoid it produced magnetic field around it.

Magnetic is field  produced by current carrying solenoids is similar to the magnrtic field  produced by magnet bar.

Note:

àMagnetic field line inside the solenoids are in the form of parrallel straight line.

The strong magnetic field produced inside a current carrying solenoids can be used to magnetized a piece of soft iron,When placed inside the solenoid the magnet thus formed is called electromagnet.the solenoid is used for making electromagnet.

NOTE:

àThe nature of coil material is used for making solenoid is soft iron ,soft iron produces strong magnetism produce.

 

 

       Electromagnet

 

An electric current can be used for  making temporary magnet known as electromagnet.

 

Q. Why we soft iron as a coal material?

The coal of electromagnet must be of a soft oeon because soft iron losses all of its magnetism when I he current in the coal is switched off. On the hand if steel is used for making coal of electromagnet this steel does not lose all its magnetism when current is switched and it becomes permanent magnet. That is why steel is not used for electromagnet.

 

Factors affect the strength of electromagnet

 

1) The no. Of turns in the coil.

2) Current flowing in the coil.

3) Lenght of air gap between it's pole. If air gap between pole is less and strength will be more).

 

 

 

 

 

Force on a current carrying conductor) In a magnetic field)

 

 

As per orested experiment current carrying exerted a force on compass needle small and deflect it from its usual position North or south. Hence we can say that current carrying wire exert mechanical force on a magnet if magnet is free move. And this force can be produced a motion in the magnet. The reverse of this is also true that is a magnet exert a mechanical force on a current carrying wire if wire is free to  move

 

 

In 1821,Paradede discovered that when a current carrying conductor is placed in a magnetic field a mechanical force is exerted on a conductor which can move the wire.

 This is known as Principal of Motor.

 

ü Experiment to demonstrate force acting on aa conductor placed in a magnetic field(Kicking wire experiment)

1)Take a small aluminium rode AB using two connecting wire suspend it horizontally from a stand .

2)Place a strong horsesue magnet in such a way that the rod AB lies between two poles with magnetic field direction upward by putting magnet north poles vertically down and south pole vertically upward.

3)Connect aluminium rod B with battery and key.

4)Pass the current through from A to B.

5)It is observed that rod is displace towards the left hand .

6)Reverse the direction of current and observed the direction of displacement of rod ,it will be now towards right.

Above experiment show that direction of force on conductor AB depend upon the direction of magnetic field.

 

1)Perpendicular to the direction of the current .

2)Perpendicular to the direction of magnetic field.

 

It is also noted maximum force is exerted on the current carrying conductor only when it is perpendicular to the direction of magnetic field.No force will will act on conductor when it is  parallel to the magnetic field.

 

FLEMING’s LEFT HAND RULE

 

Used for finding out direction of force on the current carrying conductor.

Hold the fore figure ,center fingure and thumb fingure of your left hand of right angle to each other .Adjust your hand in  such a way that fore fingure points in the direction of magnetic field and centre fingure in the direction of electric current ,then  the direction in which thumb points gives the direction of force acting on  the conductor.

 

ELECTRIC MOTOR

A motor works on the principal

Principal of Motor:

A motor walks on the principal that when rectangular coil is placed in a magnetic field and current is placed through it .A force on a coil act which rotates the coil continuously .As per Flemings left hand Rule.

 

 

 

Construction of motor

 

An electric motor consist of rectangular coil ABCD of insulated copper wire.The coil is placed between two poles of magnetic field such that arm AB and CD ,arm perpendicular to the direction of magnetic field of coil are connected to the two halves P and Q of split rings .The inner side of these halves are insulated and connected to an axel.The external conducting edges of P and Q touches two conducting brushes  X and Y .The function of X and Y is to keep conduct with the rotating rings splitting to supply the current to the coil.

Working Of Motor

à Current in the coil ABCD enters from the source battery through conductivity brush X wire splitering P which rotates along with coil ABCD and current flow back to the battery through brush Y via split ring Q .currentCurrent in arm AB of coil flows from A to B and in arm CD flows from C to D which is opposite to the direction of current in arm AB. Applying Fleming left hand rule for the direction of force on current carrying conductor in an magnetic field, we find that the force acting on arm AB pushes downward while force acting on arm CD pushes it upward thus coil and axle rotate anticlock wise. At half rotation Q makes contact with brush X and P with brush Y. Therefore the current in the coil gets reverted and flow along the path DCBA and this half axle and coil rotate anticlock in the reverse of current. This process is repeated every  after half rotation. Side AB to CD and CD to AB interchanges and coil keeps rotating anticlock wise.

 

 

 

 

 

 

·     Commercial uses of motor

1) A powerful electromagnet is used in place of permanent magnet.

2) The coil is wound on the soft iron coil. The soft iron coil magnetised and increases the strength of magnetic field.

Armeture -The assembly of soft iron coil and coil is called Armeture.

 

3) The coil contains a large no.  of insulated copper wire.

 

 

 

 

Ø     Electromagnetic Induction

 

In 1831,Micheal Farady studied that electric current can produce magnetism. The reverse of this i. e, magnetism can produce electricity.

 

The production of electricity from magnetism is called electromagnetic induction for example when a straight wire move rapidly between the two poles of horsesue magnet the electric current in produce in the wire. (Or by moving a magnet in a coil is called induces current).

The process of electromagnetic induction has lead to construction of generator.

 

 

 

Galvanomter

 

It is an instrument which can detect the presence of electric current in the circuit it is connected in series in the circuit.

 

When no current is flowing in the circuit the point of galvanomter at 0 at the centre of scale.

 

Demonstrate of electromagnetic induction

 

1) we have a straight AB hold between the poles North and South of horsesue magnet to ends of wire is move rapidly upward between the poles which causes deflection in the galvanomter means current is produced in the wire. When wire is moves downward rapidly the galvanomter pointer will move in reverse direction means current produced in the wire.

From the above experiment it shows that direction of induced current can also be reverse by reversing the direction of magnetic field. As well as reversing the motion of wire.

 

Farady and Henry Observation

 

1) A current is indicef in a coil when it is moved /rotate relative to the fixed magnet.

2) A current us also induce in a could when magnet is moved relative to the fixed.

3) No current is induced when coil and magnet both are stationary.

4) When the direction of motion of coil is reversed then the direction of induced current also get reversed.

 

 

Magnitude of Current induced in the coil can be increase

 

1) By binding rhe coil on the soft iron coil.

2) By increasing the no. Of turns in the coil.

3) By increasing the strenght of magnet.

4) By increasing the speed of rotation of the coil.

 

 

 

Q. Why a change in current in coilA induces current in coil B?

Q.Why change in current in coil A ,induces current in coilB?

 

Ans. When we switch on current it becomes electromagnet field around coil B, the effect is just same as pushing a magnet in coil B induces current flows in coil B. Momentarily, when the current in coil A study, it magnetic field is also becomes steady and current in coil B stopped.

 

Fleming Right Hand Rule

 

 

Direction of induced current produced in a straight wire moving in a magnetic field is giving by fleming right hand rule.

'Hold the thumb, fire fungure, and centre fingure of your right hand at right angle to one another. Adjust your hand such a way that fore fingure points in the direction of magnetic field, and thumb in the direction of motion of conductor, then direction of induced current in which centre fingure points.

 

The induces current is found to be highest when the direction of motion of coil is at right angle.

 

v     Direct current and Alternative current

 

1) DC-It is flow only in one direction called direct current. The positive and negative quality of DC is fixed.

Exp-dry cell, battery, etc.

 

2) AC-If the current reversed direction after equal interval time it is called alternative current. Thus, positive and negative quality of AC is not fixed.

exp-house, car alternater.

 

Advantage of AC over DC is AC can be transmitted over long distance. Without much loss of electrical.

 

 

Electric Generator

 

 

The electric generator convert mechanical energy convert into electrical energy.

Principle-

Electric general works on the principal that when a straight conductor is moved in a magnetic field, then current is induced in the conductor.

 

 

AC generator construction in electric generator-

 

An electric generator as shown in fig. Consist a rotating rectangular coil ABCD placed between two poles of permanent magnet, the end of coil are connect with R1, and R2, the inner side of thses ring are connected with brushes B1 and B2 ate kept pressed seperatly on the ring R1 and R2 internally attached to an axle. The axle may be mechanically rotate from the outside to rotate the coil inside the magnetic field. The outer end of two brushes are connected to the galvanomter.

 

 

Working-

When the axle attached to two rings is rotated such that arm AB moves up and arm CD moves down in the magnet ic induction  field produced  y permanent magnet and the coil ABCD is rotate clock wise by applying Fleming’s Right t Rule induced current flow on the direction of A to B and Cto D if there are large number of turns in each coil then current generated in each turns  and to give a large current and current flow from B1 to B2 ,After half rotation arm CD moves up and arm AB down as a result direction of current in both arm changes giving rise to the net induced current in the direction DCBA the current flow from B2 to B1 in the external circuit thus after half rotation the path of current their respective arm changes direction after equal interval of time that is called Alternative current .

 

NOTE ;To get current which does not change its direction with  time a split ring type compotater must be used with this arrangement one brush all time contact with arm moving up.

 

DOMESTIC ELECTRICAL CIRCUIT

From the electrical pole two thick copper /aluminium wire insulated L means live wire ,red colour,Neutral wire Black colour,Whereas N having neutral wire ground potential of zero 0 volt ,where livewire has potential of 220 volt there is no harm if we touch the neutral wire the two wires coming out of meter are connected to main switch .After main switch there is no another fuse usually there is called consumer fuse usually there are two separate circuit in the house lighting circuit with 5 Ms fuse and power circuit 15A fuse.The lighting circuit for low power rating such as Bulb ,fan T.V ,tublight,etc.which draw a small current in the another hand power circuit is for running high power rating devices such as iron,heater,gizer,refrigerator ,ac,etc.draw heavy current .socket used of 15Ms.

 

Electrical Safety Devices

·      To wide risk of electrical shock the metal body of an electrical body of an electrical appliances is earthed ,Green wire used for earthing.

 

Electrical Fuse

àA fuse is a safety device having a short length of a thin ,tin -plated copper wire having low melting point which melts and breaks the circuit if the current exceed a safe value .A fuse wire is connected series in the electrical current .A pure copper wire can’t be used as a fuse wire because it has high melting point .Fuses are also used to protect industrial domestic electrical appliance from damage which may be caused  due to excessive current flow due to overloading.